1. Field of the Invention
This invention relates generally to packaging apparatus, and is particularly concerned with apparatus for closing and sealing the ends of containers of thermoplastic coated paperboard material, or the like, by vibration welding.
2. Description of the Prior Art
Until recently, the conventional manner of sealing cartons or containers of thermoplastic coated paperboard material, or the like was to prebreak the end closure panels of the container and then apply sufficient heat to activate the thermoplastic coating of the various closure panel areas and then bring them together to heat seal them in a closed position. When the thermoplastic material cools and sets, the layers are sealed and adhesively secured together. In addition to requiring the use of elaborate and expensive apparatus for generating the considerable amount of heat energy required, elaborate apparatus, methods and systems are also required to dissipate the excess heat from the plant in which the packaging operation is being carried out. Examples of this general type of packaging apparatus are shown in U.S. Pat. Nos. 3,002,328; 3,120,089; 3,166,994; 3,187,647; 3,239,995 and 3,309,841.
U.S. Pat. Nos. 3,905,280 of Sept. 16, 1975 and 3,910,014 of Oct. 7, 1975 disclose apparatus for sealing the ends of thermoplastic coated paperboard container by vibration welding wherein mechanical energy is converted into localized heat energy to minimize the amount of heat and energy required, and to eliminate the necessity for expensive systems and methods for dissipating the excess heat. U.S. Pat. No. 3,526,792 discloses a transducer having a converter for converting electrical energy into mechanical energy, and a concentrating horn for concentrating the mechanical energy into vibrations at a desired frequency. In the above mentioned U.S. Pat. Nos. 3,905,280 and 3,910,014, the concentrating horn of the vibration welding apparatus vibrates at a predetermined frequency (determined generally by the configuration of the horn) when energized, and cooperates with an anvil or back-up member to clamp the layers of the thermoplastic coated paperboard between the working surface of the horn and the back-up surface of the anvil. When the layers of the thermoplastic coated paperboard material are clamped between the horn and anvil, the vibration of the horn activates the thermoplastic coating to cause the thermoplastic material to flow so that when the vibration is terminated, the thermoplastic material will cool and set to form a seal between the layers and adhesively secure the layers together throughout the area of the seal. Among the advantages of the utilization of vibration welding is that the heat generated by the vibration of the horn is concentrated in the area to be sealed, and little excess heat is required to be generated to perform the welding operation thus eliminating the requirement for some of the elaborate apparatus for dissipating the excess heat.
The above referred to U.S. Pat. Nos. 3,905,280 and 3,910,014 disclose apparatus for closing and sealing thermoplastic coated paperboard containers or cartons both of the type having a so-called "gabled" top having, in its closed condition, upwardly inclined panels projecting from the top edges of the sides of the container, as well as such containers having a flat top. Both types of containers generally have a tubular body, of rectangular or other cross section, with an end closure having front, rear and side panels that extend axially from the tubular body when the end closure is in is fully open position. The end closure is generally folded by closing means to a closed position with the side panels at least partially collapsed between the front and rear panels, and with sealing strips projecting axially outwardly from the front, rear and side panels of the end closure. With a flat top container, the front and rear panels of the end closure lie substantially flat and transversely of the tubular body when the end closure is closed with the side panels collapsed beneath the front and rear panels, and the sealing strips and a closure flap on the panels (as shown in U.S. Pat. No. 3,910,014) projecting axially outwardly from the container body at the junction between the front and rear panels. The sealing strips are then welded together to seal the end of the container and secure the end closure in its closed condition. With a gabled top container, the front and rear panels are inclined with respect to the axis of the tubular body of the container as mentioned above.
In the apparatus disclosed in U.S. Pat. No. 3,910,014, the cartons or containers are sequentially conveyed through a closing station, a welding station, and a closure flap heating, folding and welding station. A pair of opposed closing jaws are located at the closing station, which closing jaws are movable toward each other from an open position to a closed position to fold the open end closure panels of a container received therebetween to the closed condition. An anvil and vibration welding device is located at the welding station. When a container moves to the welding station from the closing station, a vibrating horn extends from the vibration welding device and engages one outer surface of the sealing strips while forcing the other outer surface of the sealing strips into engagement with the anvil. The horn vibrates at a frequency sufficient to activate the thermoplastic material to flow. When the thermoplastic material cools and sets, the layers of the sealing strips are welded together and the end of the container is sealed. The container then moves to the closure flap heating, folding and welding station where the closure flap is heated and folded flat over the closed top.